Baghdad, Iraq ? Iraqi police backed by U.S. coalition troops raided a mosque before dawn Tuesday in the holy city of Karbala, arresting dozens in a clampdown on Shiite Muslim militants. Outside the Sunni Muslim city of Fallujah, meanwhile, insurgents struck U.S. forces for a third straight day.

The continuing attacks on the U.S. occupation army produced no new reported casualties Tuesday, as Washington prepared for a pivotal conference in Madrid to win international aid to rebuild Iraq — help that the Americans hope will eventually be accompanied by foreign troop reinforcements.

The latest troubles in Karbala began a week ago over ownership of a bus, but reflect a power struggle between armed followers of militant Shiite cleric Muqtada al-Sadr, who demands an immediate U.S. withdrawal from Iraq, and gunmen loyal to religious leaders who take a more moderate stand toward the Americans.

Al-Sadr’s group occupied a mosque in the shrine city amid clashes that officials of the U.S.-led coalition said left three Iraqis dead and 50 wounded.

With the endorsement of Karbala’s senior clerics, Iraq’s interim Governing Council decided to take action against the al-Sadr forces, said interim Interior Minister Nori al-Badran.

The raid went smoothly, he said. “All the gunmen surrendered with their weapons. Twenty-one people were arrested. Another 20 guarding outside the mosque were arrested, too.”

Occupation spokesman Charles Heatly, of the Coalition Provisional Authority in Baghdad, said the police raiders “seized a number of weapons. These are criminal elements who are accused of taking over the mosque.”

The U.S. command said American forces were at the scene to provide support if necessary.